Previously proposed technologies disclosed, for instance, in JP-A-2006-318784, JP-A-2005-100952, and JP-A-9-259913 use a plurality of current sensors installed in a plane parallel to that of power generation by a fuel cell, and reflect the results of partial current measurements taken by the current sensors in system control. The technologies disclosed in such patent documents individually compare partial currents measured at various measurement points against a predetermined reference value or compare a current distribution pattern obtained by consolidating the measured values against a predetermined reference pattern, and examine the results of comparison to detect an abnormality such as dry-up, flooding, fuel gas deficiency, or oxidant gas deficiency.
The term “dry-up” denotes a phenomenon in which the fuel cell has a low internal water content, thereby allowing an electrolytic film to dry. The electrolytic film of the fuel cell requires water molecules to move internal hydrogen ions, and exhibits high ionic conductivity only when it contains water. Therefore, if the electrolytic film is dry due to the low water content of the fuel cell, the ionic conductivity decreases to significantly degrade the power generation performance of the fuel cell. To maintain the excellent power generation performance of the fuel cell, it is therefore important that the interior of the fuel cell be kept in an appropriate wet state.
A previously disclosed technology (hereinafter referred to as the prior art) described in JP-A-2006-318784 relates to the detection of dry-up (also referred to as dry-out). The prior art compares the distribution of electrical current density in an inlet flow path of cathode gas (oxidant gas) against the distribution of electrical current density in an outlet flow path. If the electrical current density in the inlet flow path is decreased, the prior art concludes that a dry-up phenomenon has occurred.